Role of beta-endorphin on phospholipase production in Malassezia pachydermatis in dogs: new insights into the pathogenesis of this yeast

In vitro activity of lactoferricin solution against Malassezia pachydermatis from otitis externa in dogs and cats

BACKGROUND

Malassezia pachydermatis is a commensal organism of the skin, yet it may induce dermatitis and/or otitis. Lactoferricin (Lfcin) is an antimicrobial peptide obtained by the pepsin-mediated digestion of lactoferrin, a multifunctional innate-defence milk protein. The antibacterial activity of Lfcin is thought to cause alteration of bacterial membrane permeability, thus inducing cell death.

OBJECTIVES

The aim of this study was to evaluate in vitro antifungal activity of different dilutions of Lfcin solution against M. pachydermatis strains isolated from ears of dogs and cats with otitis externa.

METHODS AND MATERIALS

Fifty clinical Malassezia isolates from 40 dogs and 10 cats were tested. A dilution method in microtitre plates was used starting with a 20% Lfcin water solution. The different dilutions were 2:1 (13.3%), 1:1 (10%), 1:2 (6.7%), 1:5 (3.3%) and 1:10 (1.8%). Results were expressed as the value at which the growth of 50% (minimal fungicidal concentration MFC₅₀ ) and 90% (MFC₉₀ ) of yeast cells was inhibited.

RESULTS

All strains showed susceptibility to 20% Lfcin solution (100%). With 1:5 and 1:10 dilutions corresponding to 3.3% and 1.8% Lfcin solutions, all strains showed resistance. The MFC₅₀ and MFC₉₀ values were observed at 13.3% and 20% Lfcin solutions.

CONCLUSIONS AND CLINICAL RELEVANCE

The results indicated that Lfcin solution exhibits the antimicrobial activity specific to antimicrobial peptides. In particular, the 20% solution can be effective in killing M. pachydermatis isolated strains. Some susceptibilities also are evident at lower concentrations of ≤6.7% for four strains.

Putting It All Together to Understand the Role of Malassezia spp. in Dandruff Etiology

Dandruff is a common scalp condition causing both a discomfort and an undesired social image. Various studies dating from early 1900s have investigated the condition, but understanding of underlying mechanisms and etiology of the condition is still in its infancy. Formation of dandruff is a common but complex event which has been associated with numerous causal factors. Physiological conditions such as pH, water content, or sebum secretion are some of the host-related factors. An imbalance between these factors can disturb the physiological equilibrium of the scalp that can lead to dandruff formation. However, severity of the condition is strongly related to the lipophilic yeast of the skin microbiota, Malassezia spp. On the other hand, there are recent publications highlighting the role of other scalp microbiota members on dandruff formation. This review investigates the processes leading to the formation of dandruff to provide an etiological description of the condition, with a focus on Malassezia spp.

Spondyloarthritis, Acute Anterior Uveitis, and Fungi: Updating the Catterall-King Hypothesis

Spondyloarthritis is a common type of arthritis which affects mostly adults. It consists of idiopathic chronic inflammation of the spine, joints, eyes, skin, gut, and prostate. Inflammation is often asymptomatic, especially in the gut and prostate. The HLA-B*27 allele group, which presents intracellular peptides to CD8+ T cells, is by far the strongest risk factor for spondyloarthritis. The precise mechanisms and antigens remain unknown. In 1959, Catterall and King advanced a novel hypothesis explaining the etiology of spondyloarthritis: an as-yet-unrecognized sexually acquired microbe would be causing all spondyloarthritis types, including acute anterior uveitis. Recent studies suggest an unrecognized sexually acquired fungal infection may be involved in prostate cancer and perhaps multiple sclerosis. This warrants reanalyzing the Catterall-King hypothesis based on the current literature. In the last decade, many links between spondyloarthritis and fungal infections have been found. Antibodies against the fungal cell wall component mannan are elevated in spondyloarthritis. Functional polymorphisms in genes regulating the innate immune response against fungi have been associated with spondyloarthritis (CARD9 and IL23R). Psoriasis and inflammatory bowel disease, two common comorbidities of spondyloarthritis, are both strongly associated with fungi. Evidence reviewed here lends credence to the Catterall-King hypothesis and implicates a common fungal etiology in prostate cancer, benign prostatic hyperplasia, multiple sclerosis, psoriasis, inflammatory bowel disease, and spondyloarthritis. However, the evidence available at this time is insufficient to definitely confirm this hypothesis. Future studies investigating the microbiome in relation to these conditions should screen specimens for fungi in addition to bacteria. Future clinical studies of spondyloarthritis should consider antifungals which are effective in psoriasis and multiple sclerosis, such as dimethyl fumarate and nystatin.

β-Endorphin enhances the phospholipase activity of the dandruff causing fungi Malassezia globosa and Malassezia restricta

β-Endorphin is known to stimulate phospholipase production by Malassezia pachydermatis during canine dermatoses. The role of β-endorphin in Malassezia infection in humans is not well studied. The present study compares the influence of β-endorphin on Malassezia globosa and Malassezia restricta isolated from patients with seborrhoeic dermatitis/dandruff (SD/D) and healthy controls. Malassezia isolates (five each of the two species from patients and healthy controls) were grown on modified Dixon's agar with or without 100 nmol/L β-endorphin. Phospholipase activity was quantified based on its ability to hydrolyze L-α-phosphatidylcholine dimyristoyl (phospholipid substrate). Free fatty acid was measured by a colorimetry method. In isolates from patients, the phospholipase activity significantly increased after exposure to β-endorphin (M. globosa, P = .04; M. restricta, P = .001), which did not occur in isolates from healthy controls. Moreover, after β-endorphin exposure the patient isolates had significantly higher (P = .0004) phospholipase activity compared to the healthy control isolates. The results suggest that isolates of M. globosa and M. restricta from patients may differ from those of healthy humans.

[Phospholipase and proteinase production by Malassezia pachydermatis isolated in dogs with and without otitis]

BACKGROUND

Malassezia pachydermatis is part of the skin microbiota of dogs and cats. M. pachydermatis has been associated with external otitis and seborrhoeic dermatitis, reported more often in dogs than in cats. When the physical, chemical or immunological mechanisms of the skin are altered, M. pachydermatis could act as a pathogen. Thus, several virulence factors, such as the ability to produce esterase, lipase, lipoxygenase, protease, chondroitin sulphatase, and hyaluronidase, have been studied.

AIMS

In the present study, we aim to identify the phospholipase activity measured at pH 6.3, and the proteinase activity measured at pH 6.3 and pH 6.8 (pH from ears of dogs with external otitis) of M. pachydermatis strains isolated from dogs with and without external otitis.

METHODS

The phospholipase activity was measured using a semi-quantitative method with egg yolk, and the proteinase activity with a semi-quantitative method using bovine serum albumin agar. The study was performed on 96 isolates of M. pachydermatis, 43 isolated from dogs without clinical symptoms of otitis, and 52 isolated from dogs with otitis.

RESULTS

In our study, 75.8% of the isolates showed phospholipase activity at pH 6.3, and 81 and 97.9% of them showed proteinase activity measured at pH 6.3 and 6.8, respectively. A higher phospholipase activity was detected in strains isolated from dogs with otitis. The proteinase activity was increased at a pH of 6.8 (97.9%) in comparison to a pH of 6.3 (81%).

CONCLUSIONS

Our results suggest that the phospholipase activity may play an important role in the invasion of host tissues in chronic canine otitis cases. The proteinase activity results obtained in this study suggest that a reduction in the pH of the treatment may improve its efficacy in the resolution of M. pachydermatis otitis.

Assessment of the antifungal susceptibility of Malassezia pachydermatis in various media using a CLSI protocol

The microdilution antifungal method (CLSI BMD, M27-A3) was used for testing the antifungal susceptibility of Malassezia species. However, optimal broth media that allow sufficient growth of M. pachydermatitis and produce reliable and reproducible MICs using the CLSI BMD protocol are yet to be established. In this study, the susceptibility of M. pachydermatis isolates to ketoconazole (KTZ), itraconazole (ITZ) and fluconazole (FLZ) was evaluated in vitro by the CLSI BMD test using Christensen's urea broth (CUB) and mRPMI 1640 containing lipid supplementation, Sabouraud dextrose broth with 1% tween 80 (SDB), and Dixon broth (DXB). A FLZ-resistant M. pachydermatis was generated in vitro and tested under the same conditions. A good growth of M. pachydermatis incubated for 48 and 72 h, respectively, was observed in CUB, SDB and DXB and not in mRPMI 1640 (p<0.001). No statistically significant differences were detected between the MIC values registered after 48 h and 72 h incubation. ITZ displayed lower MIC values than KTZ and FLZ regardless of the media employed. A large number of FLZ-resistant Malassezia strains (86.6%) was observed using DXB. A MIC>64 mg/L was observed only when the FLZ-resistant M. pachydermatis isolate was tested in SDB. Based on the results obtained herein, culture in SDB, stock inoculum suspensions of 1-5 × 10(6)CFU/ml, and an incubation time of 48 h are proposed as optimal conditions for the evaluation of the in vitro antifungal susceptibility of M. pachydermatis using a modified CLSI BMD protocol.

The Malassezia genus in skin and systemic diseases

In the last 15 years, the genus Malassezia has been a topic of intense basic research on taxonomy, physiology, biochemistry, ecology, immunology, and metabolomics. Currently, the genus encompasses 14 species. The 1996 revision of the genus resulted in seven accepted taxa: M. furfur, M. pachydermatis, M. sympodialis, M. globosa, M. obtusa, M. restricta, and M. slooffiae. In the last decade, seven new taxa isolated from healthy and lesional human and animal skin have been accepted: M. dermatis, M. japonica, M. yamatoensis, M. nana, M. caprae, M. equina, and M. cuniculi. However, forthcoming multidisciplinary research is expected to show the etiopathological relationships between these new species and skin diseases. Hitherto, basic and clinical research has established etiological links between Malassezia yeasts, pityriasis versicolor, and sepsis of neonates and immunocompromised individuals. Their role in aggravating seborrheic dermatitis, dandruff, folliculitis, and onychomycosis, though often supported by histopathological evidence and favorable antifungal therapeutic outcomes, remains under investigation. A close association between skin and Malassezia IgE binding allergens in atopic eczema has been shown, while laboratory data support a role in psoriasis exacerbations. Finally, metabolomic research resulted in the proposal of a hypothesis on the contribution of Malassezia-synthesized aryl hydrocarbon receptor (AhR) ligands to basal cell carcinoma through UV radiation-induced carcinogenesis.

Expression of the micro-opioid receptor on Malassezia pachydermatis and its effect in modulating phospholipase production

Malassezia spp. may act as opportunistic skin pathogens in humans and animals. Malassezia pachydermatis proliferation and phospholipase production may play a pathogenic role in the occurrence of skin lesions in dogs. This study investigates the presence of mu-opioid receptor (MOR) in M. pachydermatis strains isolated from healthy dogs and dogs with skin lesions and its effects on phospholipase activity (p.a.). P.a. of 64 M. pachydermatis isolates was evaluated using different concentrations of naloxone (Nx), a MOR antagonist. Isolates were divided into Group A (i.e., 40 isolates from 26 dogs with dermatitis) and Group B (i.e., 24 isolates from 12 healthy dogs). The MOR expression was analyzed by Western blot and immunofluorescence. A statistically higher p.a. than that of the controls was found with isolates in Group A at a Nx concentration of 10(-6) M (P<0.05). No isolate in Group B displayed p.a. in either control samples or in the presence of any Nx concentration. Immunoblotting revealed two positive MOR immunoreactive bands of approximately 65 and 98 kDa. MOR expression and localization was also demonstrated by immunofluorescence in isolates from Groups A and B. This study provides the first evidence of MOR expression on M. pachydermatis cell membranes pointing to its possible role in modulating p.a. production in isolates from dogs with skin lesions.

Assessing the relationship between Malassezia and leishmaniasis in dogs with or without skin lesions

The relationship among the frequency, population size and phospholipase activity of Malasseziapachydermatis was investigated for dogs with Leishmania infantum infection (Li+) and those without evidence of this infection (Li-). A group of 188 dogs (141 without and 47 with skin lesions) was examined clinically, and samples were taken for the detection of Malassezia and L. infantum using various diagnostic methods. Malassezia was cultured from skin samples from 101 (53.7%) dogs and classified biochemically and molecularly as M. pachydermatis. A significantly higher mean population size of M. pachydermatis was cultured from the skin of L+ dogs compared with L- dogs. For M. pachydermatis, most phospolipase-producing cultures and the highest phospholipase activity were recorded for L- dogs with lesions and L+ dogs without lesions. The results showed that M. pachydermatis was a common commensal on dogs with or without L. infantum infection and established that L. infantum infection in dogs without skin lesions was associated with increased growth of M. pachydermatis and production of phospholipase in vitro.